Health disparities among lesbian, gay, and bisexual (LGB) persons across the lifespan are increasingly well- documented, yet gaps remain in our basic understanding of the health status, behaviors, and outcomes within LGB groups. Specifically, bisexual women tend to fare the worst on a majority of health outcomes, with the most consistent and pronounced disparities in mental health. A potentially important area of investigation pertains to the unique identity-based stressors associated with a bisexual identity. Minority stressors at the daily-level, known as microaggressions, may be more common among bisexual women and may explain health disparities among this group. The proposed study will use daily process measures, in the form of electronic diaries (EDs), over a 4-week period, to study the effect of microaggressions on bisexual women's daily mental health. Qualitative interviews will also be conducted. In addition, we will consider lifetime stressors that may potentiate deleterious effects of microaggressions on daily health and lifetime mental health. The main hypothesis of the proposed study is that bisexual women who more frequently report sexual orientation microaggressions will experience poorer mental health than bisexual women who less frequently report such microaggressions. In order to test this, we propose the following aims: 1) determine the frequency and source of sexual orientation microaggressions (SMAs) among racially diverse bisexual women and test their association(s) with mental health, 2) identify the characteristics of bisexual women's microaggressive experiences, e.g., context, content and source, including their responses to such experiences, through both quantitative and qualitative methodologies and 3) identify lifetime stressors that influence associations between SMAs and daily health and lifetime depression. Such stressors will include: childhood sexual or physical abuse, adult sexual or physical abuse, and a history of hazardous drinking. This exploratory project relies on a novel multi-method approach to study daily-level minority stressors, in the form of microaggressions, among a relatively understudied population, bisexual women. This preliminary exploration of within-group differences can significantly advance our knowledge of the risk factors associated with mental health disparities among racially diverse bisexual women. Findings will be critical for informing directions for future research and practice through the identification of relevant research questions and/or foci for preventative interventions.